The popularity and convenience of digital cameras as well as the widespread of use of Internet communications have caused user-produced images such as photographs to become ubiquitous. For example, users can keep large private collections of images. Many users of Internet platforms and services such as email, bulletin boards, forums, and social networking services post images for themselves and others to see. In some cases, labels or tags can be associated with an image, e.g., as metadata, to indicate subjects depicted in the image.